1 Field of the Invention
The present invention relates to machining of a workpiece and, more particularly, to a method of accurately producing three dimensional shaped objects.
2 Prior Art
In the past, two tool path methods have been known and applied on turning systems for the production of hemispherical shells and other parts of rotation. One is commonly known as the X-Z method, where a single pointed tool is mounted about 45 degrees off the tool post, and two linear slides are used to guide the tool along a pre-programmed contour. Most commercially available turning systems today consist of numerous linear slides. Each slide can be controlled individually, permitting the tool to impose a predetermined shape onto the blank part. The second method, called R-Theta method, is far different from the X-Z method in that the tool is slowly rotated by a rotary slide. The tool is also mounted on a single linear slide, allowing for the tool to be re-positioned in distance from the center point of the rotary slide, thus accommodating different part sizes and shapes.
Each of these methods theoretically produces a metal chip that equals the surface area of the hemishell times the depth of cut, and therefore: 2.pi.r.sup.2 times the depth of cut. Since only a small portion of the total surface area of the part is machined away at one revolution of the part, the chip can be many feet in length, and often the chip forms into a ball or rolls around the tool or tool post. In many cases, if the chips are not removed by manual or mechanical force, this chip formation at or around the tool can damage the part surface.
In the X-Z method used in machining hemishells, since the tool is only located normal or perpendicular to the cutting surface at about the 45 degree area of the hemishell, the chip flow and the tool pressure against the surface of the part is changing continuously. On the other hand, a different area of the tool tip, or tool nose, is in contact with the part depending on the positioning of the tool during machining between the equator and the pole of the part. This imposes the tool nose radius error onto the contour of the part, whereby this tool error has been evaluated to be a major error in the manufacture of hemishell components.
The R-Theta method always keeps the tool perpendicular to the cutting surface due to its rotational motion, keeping the tool pressure at a constant. Since one edge of the tool, rather than a different portion of a radius as in the X-Z method, is interfacing with the surface to be machined, the actual tool nose radius has no influence on the part contour during R-Theta machining. Yet a large burden is placed on the tool by using the same edge to cut the entire part from equator to pole. Any tool wear at the tip of the tool results in a part contour error, where the radial distance of the hemishell gets smaller as the tool wears resulting in a change in the desired contour.
It is an objective of the present invention to provide a new and improved method of machining a three dimensional object that can remove material from a workpiece in predetermined shapes and sizes and can produce several types of cuts at short intervals.